Delayed opening parachute pack



Jan. 10, 1961 Filed Nov. 15, 1949 FIG.l.

3 Sheets-Sheet 1 Jan. 10, 1961 G. L. FOGAL ETAL 2,967,686

DELAYED OPENING PARACHUTE PACK Filed Nov. 15, 1949 3 Sheets-Sheet 2 FIG. 3.

c. L. FOCAL c. B. BROWN Jan. 10, 1961 G. L. FOGAL ETAL DELAYED OPENING PARACHUTE PACK 3 Sheets-Sheet 3 Filed NOV. 15, 1949 FIG.7.

awe/Mow G. L. F OGAL G. B. BROWN may 2,967,686 DELAYED OPENING PARACHUTE PACK Gordon L. Fogal, 2607 Parker Ave., Silver Spring, Md.,

and Graham B. Brown, 144 Moncure Drive, Alexandrla, Va.

Filed Nov. 15, 1949, Ser. No. 127,471 8 Claims. (Cl. 244-150) (Granted under Title 35, U.S. Code (1952), sec. 266) This invention relates to parachute packs and more particularly to a release device for a parachute pack which adapted to open the cover of the pack to release the parachute therefrom and thereafter render the parachute effective to decelerate the descent of the mine after the mine has been released from an aircraft in flight and fallen free through the air to a preselected distance above the surface of the earth whereby the mine may be released from great heights and planted within a target area with a high degree of accuracy.

In our copending application for Delayed Opening Parachute Pack, Serial No. 114,444, filed September 7, 1949, now U.S. Patent 2,812,148, there is described and claimed a mechanism for releasing a parachute from a casing which is arranged to be operated to close a pressure switch to initiate operation of the parachute release mechanism in response to a preselected barometric pressure thereon as the mine and parachute reach a predetermined distance above the surface of the earth. While the barometric pressure responsive release mechanism is effective to release the parachute at a preselected altitude above a target area when the barometric pressure at that altitude may be measured, or is known, the barometric pressure changes from time to time and it is not always possible under actual service conditions to determine accurately what the barometric pressure might be at a specific altitude above the target area.

According to the arrangement of the present invention, an F-M altimeter operable on the principle of reflected radiated energy is employed as an alternative means for operating the release mechanism of our aforementioned patent application, the altimeter being arranged to close a switch which has been connected in parallel with the barometric pressure responsive switch when the altitude measured by the altimeter corresponds to the preselected distance above the surface of the earth at which it is desired to release the parachute by operation of the barometric pressure responsive switch. When the mine is planted from a great altitude, its descent is substantially vertical and the parachute is usually released by operation of the more accurately operable altimeter, whereas, when the mine is planted at a relatively low altitude, the mine trajectory has a forward component, the altimeter does not provide a true measure of altitude for reasons hereinafter disclosed, and the release mechanism is usually operated in response to barometric pressure.

By reason of the aforedescribed dual or alternatively operative arrangement of the present invention for releasing the parachute, release thereof at the desired altitude is more positively assured.

One of the objects of the invention is to provide a release mechanism for a mine parachute which will retain the parachute within the casing until a predetermined interval has elapsed after the mine has fallen free of the launching aircraft and the barometric pressure has reached a predetermined value or the mine has reached a predetermined distance above the surface of the earth rates atent O as measured by a predetermined change in a reflected energy condition, selectively according to which condition occurs first.

Still another object of the present invention is to provide a release mechanism for a mine parachute which will retain the parachute within a casing until the lapse of a predetermined period of time after the barometric pressure on the mechanism reaches a predetermined value corresponding to a predetermined distance above the surface of the earth or a reflected energy condition reaches a predetermined value corresponding to this distance, selectively in accordance with the order of the occurrence of these conditions.

Another of the objects resides in the provision of a new and improved device for releasing a cover and parachute from a parachute casing in which the release is effected by I firing an explosive charge at the termination of a predetermined interval after the atmospheric pressure reaches a preselected value or the device reaches a predetermined measured distance above the surface of the earth, selectively in accordance with the order of the occurrence of these events as the device descends from the launching aircraft.

A still further object of the present invention resides in the provision of a mechanism for releasing a parachute from a parachute casing which may be operated in response to barometric pressure or in response to the degree of frequency modulation of energy radiated from the mechanism and reflected from the earths surface.

A still further object is to provide a parachute release mechanism for ejecting a parachute from a casing which is operable in response to either of two conditions indicative of the distance of the mechanism above the surface of the earth whereby release of the parachute at a preselected altitude may be positively assured by the true response of the mechanism to at least one of the conditions.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. 1 is a side elevation, partly broken away, of the parachute pack and mechanism for releasing the cover therefrom according to the preferred form of the invention;

Fig. 2 is a somewhat enlarged sectional view of a barometric pressure responsive switch employed in connection with the present invention for partially closing the firing circuit thereby to render the firing circuit effective for releasing the cover from the parachute casing when the firing circuit becomes fully closed a predetermined interval after the atmospheric pressure on the switch reaches a preselected value;

Fig. 3 is a somewhat enlarged sectional view of the arming switch of the present invention for closing a portion of the firing circuit as the mine is released from the launching aircraft;

Fig. 4 is a somewhat enlarged sectional view of the cover latch which releasably \locks the cover to the parachute casing;

Fig. 5 illustrates in diagrammatic form the firing circuit employed in connection with the present invention which operates to render the locking means effective to release the parachute from the parachute casing when the circuit becomes fully closed a predetermined interval after the atmospheric pressure reaches a preselected value corresponding to a predetermined distance above the surface of the earth or the frequency modulation of energy radiated from an altimeter reaches a predetermined value corresponding to this distance selectively in accordance with the order of occurrence of these conditions; i

Fig. 6 is a plan view of the retaining ring employed in connection with the cover latch for releasably locking the cover to the parachute casing; and

Fig. 7 is a diagrammatic view illustrating two different types of trajectories assumed by the mine as it falls free of the launching aircraft at two diflerent altitudes and illustrating an effective and also an ineffective condition of operation of the F-M altimeter respectively.

Referring now to the drawings in which like numerals of reference are employed to designate like parts throughout the several views and more particularly to Fig. 1, there is shown thereon a mine generally designated 1d of a type adapted to be released from an aircraft in flight and having a flanged portion 11 and a cylindrical portion 23 formed on the tail of the mine. A securing ring 12 having inwardly extending flange portions 13 and 14 lock the securing ring to the flange portion 11. Securing ring 12 is also provided with a release device, generally designated 115, which is adapted to operate to release the mine from the securing ring 12 as the mine enters a body of water, the structure and operation of the release device being more fully set forth in the copending application of Alvin C. Hall et al. entitled Parachute Release Mechanism filed April 2'0, 1949, Serial Number 88,872, new U.S. Patent 2,502,455. Securing ring 12 is also provided with a plurality of members 15 spaced along the ring, secured thereto and extending vertically therefrom, each of the members having a bolt 16 secured to the member for attaching the looped ends 17 of the shroud lines 18. Each of the members 15 is provided with a grooved portion 19 for receiving the crimp 21 formed about the side of the parachute casing 22 for securing the casing to members 15. Casing 22 is formed with an inwardly extending crimped portion 24 for providing a seat for an interfitting cover 25 for enclosing a parachute 26. Cover 25 is provided with an eye bolt 107 secured thereto in any well known manner for receiving a looped end of the static line 106, the other end of the static line (not shown) being stitched to the crown of the parachute 26. Casing 22 is also provided with vertical fins 112 for guiding the mine 10 through the air as the mine descends from the launching aircraft and slots 27 formed in the rim of the casing for receiving the shroud lines 18 therein, the other ends of the shroud lines (not shown) being stitched to the hem of the parachute 26. Pins 112 are also provided with laterally extending supports 116 and 117 which are riveted or otherwise secured to the fins for supporting receiving antenna 118 and transmitting antenna 119 respectively. Conductors 132 and 133 form an electrical connection from antennae 113 and 119 respectively to the radar altimeter 123.

The casing 22 is formed with an inwardly extending portion 121 to which is bolted a base plate 28 and casing 29 for enclosing various mechanisms for releasing the cover 25 and the parachute 26 from the casing as one of the release devices operates in response to atmospheric pressure of predetermined value or as a second one of the devices comprising the aforementioned radar altimeter 123 operates as the mine reaches a preselected distance above the earth and at the expiration of a predetermined interval of time selectively in accordance with the order of occurrence of operation of these release devices.

Base plate 28 has a storage battery 122 and a F-M radar altimeter 123 bolted thereon and is provided with an inwardly extending portion forming a centrally disposed opening 31 which is closed by plate 113 bolted to the flange portion. Plate 113 is provided with an axial opening 114, Fig. 2, through which'is slideably arranged a tubular threaded adjusting bolt 32. The inner end of the adjusting bolt 32 is provided with an outwardly extending flange portion 33 on which is secured in airtight relation 21 non-conducting cover 34 having a pair of electrical contacts 35 and 36 molded within the cover 34. The contacts 35 and 36 are provided with a pair 4 of conductors 84 and which extend through bolt 32 and outwardly therefrom. An inner flexible metallic bellows 37 is formed in air-tight relation with flange portion 33, cover 34, and base disk 38. A outer flexible bellows 39 is formed in air-tight relation with base disk 38 and cover plate 41 to form a sealed chamber 42 which has a substantial amount of air evacuated therefrom to form a partial vacuum within the chamber 42. The cover plate 41 has secured thereto, as by welding, brazing, or the like, a cup member 43 into which is molded insulating washer 44 with a set screw 46 engaging the washer and electro conducting contact bridge disk 45 to secure the parts together. Adjusting bolt 32 is in threaded engagement with adjusting nut 47 for adjustably positioning contacts.

35 and 36 with relation to contact disk 45. Compression spring 48 is disposed under compression between cover plate 41 and the base disk 38 to yieldably urge the cover plate away from the disk. A second corn pression spring 49 disposed about bolt 32, interposed under compression between base disk 38 and flange portion 33 to yieldably urge contacts 35 and 36 into engagement with contact disk 45.

It may be readily seen that as the atmospheric pressure surrounding bellows 39 is increased to compress the bellows 39, contact disk 45 will move into engagement with contacts 35 and 36 to form an electric connection be tween conductors 84 and 85 when the atmospheric pressure reaches a predetermined value. In accordance with the arrangement of the present invention the aforedescribed switch arrangement comprises a barometric pressure responsive device generally designated 108 for partially closing the electric circuit, Fig. 5, when the barometric pressure surrounding the device reaches a preselected value to initiate operation of the parachute release mechanism as will hereinafter be more fully described.

Cover 25 is provided with a centrally disposed opening 51 as shown in Fig. 4 for receiving threaded portion 52 of housing 53. Threaded portion 52 engages lock nut 54 for clamping housing 53 to the cover 25. Housing 53 is provided with an axial bore 55 and an innerconnecting reduced bore 56 to form a shoulder at 86. Slideably arranged within bore 55 is a cylindrical portion 59 of the release member 62 which is provided with a plurality of horizontally disposed cylindrical openings 61 into which are loosely fitted locking balls 58. A pair of centering pins 63 slideably arranged within suitable bores formed within housing 53 and release member 62 are provided for assembling the parts in alignment with each other. Release member 62 is provided with a threaded extension 87 disposed through suitable opening 64 formed in casing 29 with a lock nut 65 engaging extension 87 for securing release member 62 to the casing 29. Slideably arranged within the cylindrical bore of release member 62 is a spool-shaped release piston 66 having a cylindrical extension 67 formed thereon. The extension 67 is provided with a peripheral groove 68 formed thereon for receiving the inwardly extending projections 88 of yieldable retaining ring 69, shown more clearly in Fig. 6, which engages shoulder 86 when the parts are in the assembled position of Fig. 4. Spool shaped release piston 66 is provided with a necked-down portion 89 and a pair of enlarged piston portions 71 and 72 slideably arranged within the cylindrical bore of member 69, piston portion '71 being arranged to retain locking balls 58 within groove 57 when assembling the parts together. Release member 62 is provided with an internally threaded portion 73 for threada'oly engaging detonator housing '74. Detonator housing 74 is provided with an axial bore 75 into which is slideably arranged piston 76 and cylindrical portion 77 of the detonator casing 78.

The mechanism for initiating the operation to release the cover from the parachute casing comprises an electroresponsive firing device or detonatingunit formed of a heating element 79 molded within a pyrotechnic substance 81 adapted to ignite when heated by the heating element; a time delay element. 82 adapted to burn along its length for a predetermined interval such, for example, as two seconds after being ignited and to thereafter fire the explosive mixture 83 after the element 82 has burned along its length. The pyrotechnic substance 81, time delay element 82, and explosive mixture 83 are molded within the cylindrical portion 77 of the detonating casing 78 and is arranged to abut piston 76. Conductors 84 and 110 connected to heating element 79 extend outwardly of the detonator casing 78, one of the conductors 84 being connected to terminal 36 of the barometric pressure responsive device 108, the other conductor 110 being connected to contact terminal 92 of an arming device generally designated 91, the other terminal 93 of the arming device is connected by a conductor 111 to one side of battery 122, the other side of the battery being connected to conductor 85 to contact terminal 35 of the barometric pressure device 108.

The arming device 91 of generally cylindrical configuration is formed of phenolic material which is molded about a pair of contact terminals 92 and 93 which extend inwardly of the bore 94 provided in the arming device. The arming device 91 is bolted to the casing 29 and in registry with suitable openings 95 provided therefor for bringing terminals 92 and 93 within the casing. Arming device 91 is also provided with a piston 97 formed of electroconducting material and havinga piston rod 98 extending therefrom. Piston 97 is slideably arranged within bore 94 and interposed between terminals 92 and 93 and the base of bore 94. Sleeved about piston rod 98 and interposed under compression between piston 97 and the base formed by bore 94 is a compression spring 99 which yieldably urges piston 97 into engagement with contact members 92 and 93. Hold-off piston 101 formed of non-conducting material is slideably arranged within bore 94, the piston 101 having a depending axial projection 102 which is initially maintained in abutting engagement with piston 97 and also having a diametrical bore 103 through the piston. An arming wire 104, one end of which is secured to the aircraft structure and the other end of which is threaded through radial bores 105 in the arming device 91 and bore 103, is provided for maintaining pistons 97 and 101 depressed against spring 99 until the arming wire is extracted thereby to separate piston 97 from engagement with contact members 92 and 93.

As the mine falls free of the aircraft, arming wire 104 is withdrawn from bores 105 and 103 and spring 99 operates to move piston 97 into electrical engagement with contacts 92 and 93 to close the arming switch 91 thereby to partially arm or complete a portion of the firing circuit shown in Fig. 5.

The firing circuit also includes the aforementioned frequency modulated radar altimeter 123 which is connected in parallel with the barometric pressure device 108 by the conductors 125 and 126. Altimeter 123 may be of any type suitable for the purpose such, for example, as the type disclosed and described on pages 130 to 134 of the April 1946 issue of Electronics. For the purposes of the present invention, the article-disclosed altimeter is modified such that the aforedescribed receiving antenna 118 and transmitting antenna 119 are electrically connected thereto. The altimeter circuit disclosed in Fig. 6 on page 133 of the above publication has also been modified in the present invention by introducing a relay generally designated 124 in place of the altitude indicator, which relay is so constructed and arranged to close the relay switch contacts 137 and thereby complete the firing circuit of Fig. 5 from the battery 112 to the heating element 79 when the altimeter generates a current therein of a predetermined value sufiicient to operate the relay 124 and corresponding to a preselected distance above the surface of the earth. A variable resistance 139 preferably is shunted across the coil of relay 124 whereby the relay may be caused to close at different altitudes while requiring the same operating current, the current supplied 139 by the altimeter being proportional to the altitude. 7

As the mine descends through the air, the atmospheric pressure surrounding the mine gradually increases to compress the bellows 39, thereby to move disk 45 downwardly until the disk moves into engagement with contacts 35 and 36 as the barometric pressure reaches a pre selected value corresponding to a predetermined .distance above the surface of the earth, thereby to complete the firing circuit whereupon the heating element 79 becomes energized.

When the heating element is energized, pyrotechnic material 81, Fig. 4, is ignited to initiate the burning of time delay element 82 which burns for a preselected interval such, for example, as two seconds to then fire the explosive mixture 83. Explosive mixture 83 propels pistons 76 and 66 upward to force projections 88 of yieldable member 69 out of groove 68 in piston extension 67 and simultaneously move necked-down portion 89 into registry with balls 58 to cause the balls to move out of groove 57 to free housing 53 and cover 25 from release member 62 to propel the cover away from casing 22 and into the air stream. As cover 25 moves into the air stream, it acts as a pilot parachute to pull the static line 106 and parachute 26, secured to the line, from the casing 22 to cause the main parachute 26 to open and thereafter to decelerate the descent of the mine as the mine approaches the target area.

As shown in Fig. 7, when a mine is dropped from a high altitude, the fins 112 guide the mine such that the mine axis is substantially perpendicular to the earths surface as in the position assumed at 127. When the mine is falling free and the nose of the mine is pointed directly towards the earth, the transmitting antenna 119 projects a signal which is illustrated by the broken line 128 and which is reflected by the earths surface, as illustrated by broken line 134, and is received by receiving antenna 118 for causing the altimeter 123 to operate and close contacts 137 of relay 124 at a predetermined altitude above the earths surface such, for example, as the altitude illustrated by line 135. However, should it become necessary to release the mine from the aircraft as at 129, the mine follows a trajectory toward the surface of the earth as illustrated by the broken line 131. When the arming wire 104 is withdrawn and mine assumes a substantially horizontal position as at 129, the radiated and reflected energy, follows the broken lines 136 and 138 respectively which do not traverse distances corresponding to the true altitude. Thus, under these conditions, the parachute is released in response to barometric pressure.

In order toprevent the parachute from becoming entangled with the launching aircraft should the mine be released in a zone where the barometric pressure is greater than the setting of the barometric device 108 or the altimeter contacts are closed, the time delay element 82 is arranged to delay the release of the cover 25 and the parachute 26 until a period of time in the order of two seconds has elapsed while the mine is falling free of the aircraft. Retaining ring 69 is provided to prevent movement of the piston 66 into ball releasing position in response to shocks resulting from rough handling of What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A mechanism of the character disclosed for releasing a parachute from a parachute pack at a preselected altitude above the surface of the earth as the mechanism falls free from a launching aircraft comprising, in cornbination, a fixed cup-shaped member in which the parachute is disposed, a plurality of shroud lines on the hem of said parachute for securing the parachute to the cup member, a cover carried by said cup member and secured to the crown of the parachute for initially enclosing the parachute within the cup member to form said parachute-pack, a complementary member secured to the cover, means for releasably locking said complementary member to said cup member, an electroresponsive explosive charge arranged within said cup member in proximate spaced relation with respect to said locking means and adapted to release the locking means when the charge is fired, a battery disposed within said cup member for firing said charge as the battery is connected thereto, an F.M. radar altimeter for generating a DC. current variably in accordance with the altitude of the altimeter above the surface of the earth, and a relay controlled by said generated current and constructed and arranged to be operated thereby for connecting said electroresponsive explosive charge to said battery when said generated current reaches a predetermined value corresponding to said preselected altitude.

2. A mechanism of the character disclosed for releasing a parachute from a parachute pack at a predetermined altitude above the surface of the earth comprising, a first cup-shaped section in which the parachute is disposed and to which the shroud lines of the parachute are connected, said cup section having a plurality of fin members secured thereto and projected laterally therefrom, a second section secured to the crown of the parachute and mounted on said first section for enclosing the parachute within said first section to form said parachute pack, a slideable latch arranged within said first section and in looking engagement with said second section for releasably locking the sections together, an electroresponsive detonator arranged in substantial abutting spaced relation with respect to one end of said latch and adapted to eject the latch forcibly from locking engagement with said second section when the detonator is fired, a source of electrical energy, transmitting means including an antenna secured to one of said fin members for transmitting radar signals at a predetermined frequency toward the earth, receiving means including an antenna secured to another one of said fin members for receiving the reflected signals, and a switch controlled by said receiving means for connecting said electrical source to said detonator as the switch closed when the shift in phase between said transmitted signals and received signals reaches a predetermined value corresponding to said predetermined altitude when the free flight of the parachute and pack is substantially vertical.

3. A release mechanism of the character disclosed for releasing a parachute from a parachute pack at a preselected altitude as the mechanism falls free of the launching aircraft comprising, in combination, a casing having a parachute disposed therein and secured thereto, a cover for enclosing said parachute within said casing to form said parachute, a complementary member secured to the cover, means for releasably locking said complementary member to said casing, an electroresponsive explosive charge arranged within said casing in proximate spaced relation with respect to said locking means and adapted to release the locking means when the charge is fired, a battery disposed within said casing for firing said electroresponsive means when connected thereto, an FM. radar altimeter carried by said casing for generating a current variably in accordance with the altitude thereof above the surface of the earth, a relay controlled by said current for connecting said electroresponsive means to said battery, and a variable resistance shunted across said relay for adjusting the current supplied thereto to a value sufiicient to operate the relay when the generated current corresponds to said preselected altitude.

4. In a mechanism of the character disclosed for releasing a parachute from a parachute pack at a predetermined altitude as the mechanism falls free from the launching aircraft, the combination of a first member in which the parachute is disposed and conected to the shroud lines of the parachute, a second member carried by said first member and secured to the crown of the parachute for enclosing the parachute within said first member to form said parachute pack, means for releasably connecting said members together, said means including a connecting member arranged for actuation from a locked position to a release position, a pistol adapted to actuate said connecting member from said locking position to said release position as the pistol is fired, means including a voltage source for firing said pistol when the source is connected thereto, a frequency-modulated altimeter for generating current variably in accordance with changes in altitude, and a relay controlled by said generated current for connetcing said voltage source to said pistol when the generated current reaches a predetermined value corresponding to a preselected altitude.

5. A mechanism of the character disclosed for releasing a parchute for a mine from a parachute casing at a predetermined altitude above the surface of the earth as the mine descends from the launching aircraft comprising, a cup member secured to the mine and having the parachute disposed therein, a plurality of shroud lines secured to the hem of the parachute and said mine, a latch slideably arranged within said cup member for movement for an initial locking position to a release position, a cover carried by said cup member and secured to the crown of said parachute for enclosing said parachute in the cup member to form said parachute casing, said cover being adapted to be locked to said cup member by said latch when said latch is in said initial locking position, means for releasably locking said latch in said initial position sufficiently to prevent the movement of the latch to said release position in response to shocks received by the mine prior to launching thereof, an electrorcspcnsive explosive charge arranged within said cup member and in a substantial abutting relationship with respect to said latch for moving the latch to said release position as the charge is fired, a firing circuit including a storage battery for firing said charge when the battery is connected thereto, an arming device for partially closing said firing circuit as the mine is released from the launching craft, a frequency-modulated radar altimeter carried by said casing for generating a current variably in accordance with the altitude of the altimeter above the earth, and a relay controlled by said generated current for completing said firing circuit to the battery when the generated current reaches a predetermined value corresponding to said preselected altitude.

6. A mechanism of the character disclosed for releasing a parachute from a parachute pack at a preselected altitude above the surface of the earth as the mechanism falls free from the launching aircraft comprising, a cup member for packing the parachute therein, a plurality of shroud lines for securing the parachute to said cup member, a cover carried by said cup member and secured to the parachute crown for enclosing the parachute within the cup member thereby to form said parachute pack, locking means including a plurality of balls for releasably locking the cover to the cup member, a piston for releasably retaining said plurality of balls in the locking position thereof and adapted to be moved into a position for releasing the balls thereby to effect release of the locking means, a yieldable member in releasably locking engagement with said locking means and said piston for releasably locking said locking means to said piston, an electroresponsive explosive charge arranged within said cup member in proximate spaced relation with respect to said piston for moving the piston into position for releasing said balls from said locking position when the charge is fired, a source of electrical energy within said cup member for firing said charge as the electrical energy source is connected thereto, a pressure responsive switch for connecting said electrical energy source to said electroresponsive charge when a predetermined atmospheric pressure corresponding to said preselected altitude is applied to said switch, a frequency modulated radar altimeter for generating a current variably in accordance with the position of the altimeter above the surface of the earth, and a switch controlled by said generated current for connecting said electric energy source to said electroresponsive means when said generated current reaches a predetermined value corresponding to a preselected altitude.

7. A mechanism of the character disclosed for releasing a mine parachute from a parachute pack at a preselected altitude above the surface of the earth as the mine falls free of the launching aircraft, comprising in combination a cup member secured to the mine for disposing the parachute therein, a plurality of shroud lines on said parachute for securing the parachute to the mine, a cover carried by said cup member and secured to the crown of the parachute for enclosing the parachute within the cup member thereby to form said parachute pack, means for releasably locking said cover to said cup member, said cup member having a plurality of fin members for maintaining the longitudinal axis of the mine parallel to the line of free flight thereof, an electroresponsive explosive charge for releasing said locking means when the explosive charge is fired, a battery for energizing said electroresponsive charge as the battery is connected thereto, means including a pressure responsive switch adapted to connect said battery to said charge as the switch closes in response to barometric pressure developed thereon corresponding to said preselected altitude, a frequency modulated radar altimeter for generating current variably in accordance with the altitude thereof above the surface of the earth, said altimeter including transmitting and receiving antennae carried by said fin members and arranged thereon to direct the transmitted and received energy vertically when the axis of the mine is substantially vertical, and a current responsive switch controlled by said generated current for connecting said battery to said electroresponsive charge as said last named switch closes in response to a current of predetermined value corresponding to said preselected altitude when said mine axis is substantially vertical, said first named switch being closed first when the axis of the mine deviates from vertical sufliciently such that the reflected distance differs substantially from the altitude of the mine, and time delay measuring means included in said electroresponsive charge and constructed and arranged to delay firing thereof in predetermined time delayed relation to the closing of either one of said switches.

8. A parachute pack and parachute release mechanism for discharge of the parachute at a preselected altitude comprising, in combination, a cup-shaped parachute housing, a releasable cover carried by said housing, a complementary member secured to the cover, locking means for releasably retaining said complementary member to said housing, electroresponsive means within said housing for release of said locking means upon energization thereof, a source of electrical energy disposed within said housing and adapted to provide energization current for said electroresponsive means, an FM. radar altimeter for generating a DC. current variably in accordance with the altitude thereof above the earth, and a relay controlled by said generated current for operation to connect said electrical energy source and the electroresponsive means when said generated current reaches a predetermined value corresponding to said preselected altitude.

References Cited in the file of this patent UNITED STATES PATENTS 2,256,539 Alford Sept. 23, 1941 2,470,457 Bancora May 17, 1949 2,478,758 Frieder Aug. 9, 1949 FOREIGN PATENTS 585,265 Great Britain Feb. 3, 1947 

